“We responded to Uber's letter and will be robustly defending the legal proceedings brought by them in relation to the changes to private hire regulations," a TfL spokesperson told City A.M.

"These have been introduced to enhance public safety when using private hire services and we are determined to create a vibrant taxi and private hire market with space for all providers to flourish.”

Uber is challenging four of the new rules; requiring written English tests for drivers, having to locate its customer service call centre in London, requiring insurance that covers drivers when they are not working and having to alert TfL of changes to its business model or app.

A spokesperson for the mayor said: "Sadiq has asked his team to produce a comprehensive new strategy that will herald in a new era for the capital's taxi and private hire trades.

"Further details will be released later this year of a plan that will deliver radical improvements for customers, a boost to safety, support for the taxi trade and further improve the quality of service offered by the private hire trade. There will also be a concerted effort to make London's taxi fleet the greenest in the world."

City Hall would not be drawn on whether this would include reviewing the new regulations, agreed under former mayor Boris Johnson.

Tom Elvidge, general manager at Uber London, said: "This legal action is very much a last resort. We're particularly disappointed that, after a lengthy consultation process with Transport for London, the goalposts have moved at the last minute and new rules are now being introduced that will be bad for both drivers and tech companies like Uber."

London's cabbies, who believe the new rules do not go far enough, have also backed Uber's call for a rethink, indicating the black cab trade stood to gain from a more favourable outcome.

Other minicab firms in the capital have backed the new regulation, however.

Addison Lee chief executive Andy Boland said: “Having previously backed the proposals it’s hard to understand Uber’s resistance to implementation of these new regulations. The whole industry was fully involved in the consultation and there is a strong belief that they will benefit both passengers and drivers.”